Integrated circuits, such as memory devices, require extensive testing during fabrication to insure that a finished circuit is fully operational. This testing is performed during various stages of fabrication and may be tested while it is still part of an integrated circuit wafer. This testing is usually performed using an integrated circuit probe card which physically connects a tester to probe pads, and other electrical conductors, provided on each circuit die. The tests performed are numerous and often depend upon the type of device fabricated. These tests are often performed by placing the integrated circuit in a specific test mode of operation. While manufacturers of integrated circuits extensively test their devices using these test modes, it is desired to prohibit an end-user from placing a completed device in a test mode. As such, various methods have been devised to allow testing during manufacturing while prohibiting accidental initiation during use. These methods include, but are not limited to, electronic keys and super voltages, as known to those skilled in the art.
Some integrated circuits include voltage generator circuits which provide an internal reference voltage. For example, an integrated circuit memory device can include an internal circuit for providing a reference voltage. Prior to testing, therefore, the integrated circuit memory device must be capable of providing the internal reference voltage. The voltage generator circuit, however, often requires extensive programming prior to providing a valid reference voltage. This requirement provides a dilemma during testing. That is, a defective memory device must first be programmed to provide the internal reference voltage before it is determined that the memory device is defective. Because the procedure for setting the internal reference voltage requires numerous seconds (up to 20 seconds is common), valuable time is wasted during testing.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a method of testing an integrated circuit which does not require an internal reference voltage generator to be set prior to testing.